feat: UI interaction polish — exit animations, hover effects, directional transitions

- Add AnimatedPanel component with CSS transition-based enter/exit for
  Profile popover and Notification panel (140ms scale+fade)
- Add nav-activate-pulse animation for floating-nav active indicator (320ms glow)
- Add tool-panel-fade-in crossfade when switching ecommerce tools
- Add carousel-card-label slide-up-in 260ms on active carousel card
- Add feature-visual img hover scale(1.03)+brightness, experience-route hover translateY(-2px)
- Add community-case-card--mosaic hover scale(1.02)+shadow lift
- Add directional PageTransition: forward→slideX(20px), backward→slideX(-20px)
- Move vite proxy target from hardcoded IP to VITE_DEV_PROXY env variable
- Add .env.example for developer onboarding

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/styles/shell/app-shell.css

@@ -495,6 +495,15 @@
   box-shadow: inset 0 0 0 1px rgba(var(--accent-rgb), 0.34);
 }
 
+@keyframes nav-activate-pulse {
+  0% { box-shadow: inset 0 0 0 1px rgba(var(--accent-rgb), 0.34), 0 0 8px rgba(var(--accent-rgb), 0.25); }
+  100% { box-shadow: inset 0 0 0 1px rgba(var(--accent-rgb), 0.34); }
+}
+
+.floating-nav__button.nav-just-activated {
+  animation: nav-activate-pulse 320ms var(--ease-out-expo, cubic-bezier(0.16, 1, 0.3, 1)) both;
+}
+
 .floating-nav__button:hover .floating-nav__label,
 .floating-nav__button:focus-visible .floating-nav__label,
 .floating-nav__button.is-active .floating-nav__label {